Airbag module

ABSTRACT

The invention relates to an airbag module comprising a gas generator, diffuser and a gas bag. The invention is characterized in that the gas generator ( 5 ) is arranged in a diffuser ( 1 ) or housing of the gas generator with a stepped structure when seen in a longitudinal section. The diffuser ( 1 ) or the housing of the gas generator extends in the lower region of the side wall ( 2 ) at a distance from the gas generator ( 5 ). The lower region of the side wall ( 2 ) extends beyond the gas generator ( 5 ) in the direction of the occupant. The diffuser ( 1 ) or the housing of the gas generator ( 5 ) has a smaller cross-section than the gas generator ( 5 ). Openings ( 6,16 ) through which the gas from the gas generator flows into the gas bag ( 10 ) are arranged in a perpendicular position to the occupant. The upper ( 4 ) and lower ( 2 ) regions of the side wall are connected to each other by at least one deformable center area ( 3 ) of the side wall. One advantage provided by the inventive device is that the section of the diffuser that is located above the gas generator can, by virtue of its deformable center area, be moved out of the way of an occupant colliding therewith, thereby reducing the risk of injury.

DESCRIPTION

The invention relates to an airbag module.

From WO 96/25 309 an airbag module is known in which a diffuser ismounted above a gas generator and has a smaller cross-sectional surfacearea than the gas generator. The gas bag of the airbag module extends inthe folded state mainly at the side of the diffuser and above thediffuser there is only one layer of the gas bag. The diffuser has outletopenings mainly at the side, i.e. in a direction extending transverselyto the seat occupant.

The drawback with this arrangement is that the diffuser represents asource of danger for the occupant should he strike against the diffuserif the gas bag does not open or if the gas bag has already collapsed.

From EP 0 827 875 a steering wheel is known having a gas bag restraintsystem where the gas generator is mounted in a pot-shaped deformationelement which lies with its base above the gas generator. Openings toallow the gases of the gas generator to flow out into the gas bag areprovided in the base and at the sides of the deformation element. Thedeformation element thus likewise represents a diffuser. The gas bagextends in the folded state mainly at the side of this deformationelement and only one layer of the gas bag lies above same.

The drawback with this arrangement is that owing to the outflow openinglocated in the base there is the tendency for the gas bag to unfolddirectly in the direction of the occupant which has a negative effect onan out of position occupant. Furthermore there is no stowage spaceavailable for the gas bag above the gas generator owing to the side wallof the deformation element being only slightly inclined there towardsthe axis of the gas generator. This is particularly disadvantageous in asteering wheel on account of the small space available for the airbag.

The patent specification EP 0 773 142 A1 describes an airbag module witha gas bag, a gas generator and a diffuser which encloses the gasgenerator and has a number of perforations over the entire diffuserbody. The diffuser can hereby absorb the energy of an occupant strikingagainst same. The drawback however is that the entire diffuser body isprovided with perforations which represents an expensive solution. Inaddition the arrangement known from EP 0 773 142 A1 has the disadvantagethat there is little stowage space for the folded gas bag and the gasbag unfolds immediately in the direction of the vehicle occupant duringdeployment.

The object of the invention is to design the airbag module so that it isformed at least in part in simple manner as a deformation element wherestowage space for the folded gas bag is provided above the gas generatorand where in the first phase the gas bag unfolds mainly transversely tothe occupant.

According to this the diffuser or the housing has in the longitudinalsection a stepped construction with a lower side wall area, an upperside wall area and a central side wall area connecting the upper andlower side wall areas. The diffuser or the housing extends in a lowerside wall area at a distance from the gas generator and beyond the gasgenerator in the direction of the tear-open area of the module cover andthereby encloses at least approximately the same cross-sectional area asits section lying next to the gas generator. In this area the crosssection of the diffuser or housing of the gas generator is thus largerthan that of the gas generator. In an upper side wall area the diffuseror the housing of the gas generator has a smaller cross-section than thegas generator and in this area there are outflow openings for the gasesof the gas generator to discharge into the gas bag transversely to thelongitudinal axis of the diffuser. The lower and upper side wall areasare connected by at least one central deformable side wall area.

The arrangement according to the invention has the advantage that thesection of the diffuser lying above the gas generator can as a result ofits deformable central side wall area be shifted by the impact of anoccupant away from same so that the risk of injury is reduced. Since thelower side wall area projects upwards beyond the gas generator theadjoining central side wall area also has sufficient room for thedeformation in the direction of the gas generator. Owing to the smallercross section of the diffuser or housing of the gas generator above thegas generator there is still sufficient space above same next to thediffuser or housing in which to store the folded gas bag. Theutilization of the structural space available is thereby improved sothat the targets set for reducing the geometry of the module can beeasily met.

As a result of the openings in the diffuser or housing lyingtransversely to the longitudinal axis of the diffuser the gases enterinto the gas bag crosswise relative to the occupant and a primarilylateral unfolding of the gas bag thus takes place. The gas flow isthereby first directed upwards in the lower side wall area and strikesthe central side wall area. One part of the gas flow is diverted towardsthe outflow openings and the other part is eddied around in the spaceabove the gas generator. The multiple deflection draws energy out fromthe overall system which has a positive effect on the thermal load onthe gas bag fabric and the aggressiveness of the deployment of the gasbag.

The gas flow which is discharged from the outlet openings first forms inthe upper module area a bubble from the fabric layer located above thediffuser fabric layer located above the diffuser or housing, with thisprocess being made easier by the low package pressure existing in thisarea on account of the stepped structure of the diffuser. The bubblethen expands laterally through the stepped release of the gas bagpackage from inside to outside until fully deployed.

Owing to the lateral unfolding the extension of the gas bag in thedirection of the occupant is restricted to a minimum. The occupant isthereby not attacked in the normal position and the risk of injury tothe occupant in an out of position area is minimized. No arrester strapsor rip seams are required for the gas bag. Furthermore vibrations in thegas bag are reduced so that the gas bag occupies its optimum positionfor the protection of the occupant at an earlier moment.

The deformability of the central side wall area is preferably achievedby providing material weaknesses, more particularly in the forms ofslits, in this area. These slits thereby have a width of at leastapproximately zero millimeters so that they primarily represent nooutlet openings for the gases of the gas generator. In the case of adiffuser having a circular cross-section the slits preferably runradially.

It is expedient if the upper side wall area has a height which is lessthan half the height of the airbag module. Furthermore it is expedientif the upper edge of the diffuser or housing of the gas generatorextends practically up to the module cover. The upper side wall areapreferably has a cylindrical or conical shape.

The gas bag is preferably arranged around the diffuser and only onelayer of the gas bag is located above the diffuser.

In one embodiment preliminary outlet openings are provided in the lowerside wall area of the diffuser or housing of the gas generator toinfluence the pressure path. The preliminary outlet openings arepreferably arranged so that they do not overlap with the outlet openingsof the gas generator. They can be arranged for example above the outletopenings of the gas generator. The overall cross-sectional area of thepreliminary outlet openings should be smaller than the overallcross-sectional area of the outlet openings of the gas generator. In oneembodiment four preliminary outlet openings are provided.

The invention will now be explained with reference to the embodimentsshown in the drawings in which:

FIG. 1 is a longitudinal sectional view through a stepped diffuser;

FIG. 2 is a plan view of the diffuser according to FIG. 1;

FIG. 3 is a longitudinal sectional view through an airbag module with adiffuser according to FIG. 1;

FIG. 4 shows the airbag module according to FIG. 3 with a partiallyunfolded gas bag;

FIG. 5 shows a longitudinal sectional view through a second embodimentof the diffuser;

FIG. 6 shows a longitudinal sectional view through a third embodiment ofthe diffuser;

FIG. 7 shows a longitudinal sectional view through an airbag module witha diffuser having preliminary outlet openings.

FIG. 1 shows a diffuser which has a lower side wall area 2, a centralside wall area 3 and an upper side wall area 4 with an upper edge 4 a.The lower side wall area 2 encloses a space whose cross-sectional areais larger than that of a gas generator 5 mounted therein and extendsbeyond same towards the occupant (FIG. 3). The upper side wall area 4has a clearly smaller cross-section than the gas generator 5 and isprovided with oblong outlet openings 6. The central side wall area 3connects the lower side wall area to the upper side wall area and runssharply inclined relative to the longitudinal axis 7 of the diffuser 1.This side wall area 3 has radially arranged slits 8 whose width has atendency to zero so that these slits represent no outlet openings forthe gas discharging from the gas generator. As a result of the slits 8this side wall area 3 is deliberately weakened so that in the event ofan occupant impacting against the diffuser the wall can deform towardsthe gas generator. Since the central side wall area 3 lies at a distanceabove the gas generator 5, with this distance amounting to severalcentimeters, a space 9 is provided between the two into which thecentral side wall area 3 can deform (FIG. 3).

As can be seen from FIG. 3, owing to the stepped construction of thediffuser 1 and the thus smaller cross-section of the diffuser in thearea of the upper side wall 4 compared to the gas generator 5 a foldedgas bag 10 can lie at least in part more or less above the gas generator5 without the drawbacks which arise during unfolding which normallyoccur in the case of a gas bag folded over the gas generator. The gasbag 10 is mounted inside the module cover 12 with the folds 11 alignedin the direction of the occupant. Only one layer 13 of the gas bag 10 islocated above the diffuser, formed in the case of a gas bag comprisingan upper part and lower part, by the said upper part.

After ignition of the gas generator 5 the gas stream discharged fromsame is directed upwards at the lower side wall area 2 and strikes thecentral side wall area 3. One part of the gas flow is diverted theretowards the outflow openings 6 whilst another part is eddied around inthe space 9 above the gas generator. AS a result of this vortex a partof the energy of the gas flow is broken down so that the thermal load onthe gas bag fabric is reduced and the gas bag deploys less aggressively.The path of the gases is marked by the arrows in FIG. 3.

The gas flow leaves the diffuser 1 in the radial direction and initiallyforms in the upper module area a bubble 14 from the layer 13 of the gasbag 10 lying above the diffuser 1. This process is facilitated by thelower package pressure existing in this area as a result of the steppeddiffuser. In this first phase of deployment the module cover 12 of theairbag module 17 is ripped open by the bubble 14. The bubble 14 thenexpands laterally through the stepped release of the gas bag packagefrom inside outwards (FIG. 4) until fully unfolded.

A further embodiment of the diffuser is shown in FIG. 5 in which thelower side wall area 2 has an upper section 15 which is inclined onlyslightly relative to the longitudinal axis 7 of the diffuser. Thissection is then adjoined by the central side wall area 3.

FIG. 6 shows a stepped diffuser in which instead of the oblong outflowopenings of the embodiments previously described there are two rows ofsuperposed circular outflow openings 16.

In FIG. 7 an airbag module is illustrated in which the diffuser has fourpreliminary outflow openings 18 which are arranged above the outflowopenings 19 of the gas generator 5, i.e. these outflow openings and thepreliminary outflow openings do not overlap each other. The pressurepath in the gas bag can be additionally influenced by means of thesepreliminary outflow openings 18.

What is claimed is:
 1. Airbag module having a gas bag, gas generator anda module cover having a tear-open area is arranged above the gasgenerator wherein the gas generator is mounted essentially coaxially ina diffuser which encloses the gas generator and is provided with outflowopenings, and the diffuser extends in a side wall area at a distancefrom the gas generator, the side wall area thereby extends beyond thegas generator upwards towards the tear-open area of the module cover andencloses at least substantially the same cross-section as a side wallarea adjacent the gas generator; wherein the diffuser has a steppedconstruction with a lower side wall area, an upper side wall area and acentral side wall area which connects the upper wide wall area and thelower side wall area and which defines a step therebetween, wherein thelower side wall area extends a distance from the gas generator andbeyond the gas generator towards the tear-open area of the module cover,the diffuser has in an upper side wall area a smaller cross-sectionalsurface than the gas generator and in this area the outflow openings areprovided for the gases of the gas generator to discharge into the gasbag transversely to a longitudinal axis of the diffuser, and wherein thecentral side wall area is deformable relative to the upper side wall andthe lower side wall.
 2. Airbag module according to claim 1 wherein thecentral side wall area has material weaknesses.
 3. Airbag moduleaccording to claim 1 wherein the upper side wall area has a height whichis less than half the height of the airbag module.
 4. Airbag moduleaccording to claim 1 wherein the upper side wall area runs cylindrical.5. Airbag module according to claim 1 wherein an upper edge of thediffuser extends practically up to the module cover.
 6. Airbag moduleaccording to claim 1 wherein the gas bag is arranged around the diffuserso that only one layer of the gas bag is located above the diffuser. 7.Airbag module according to claim 1 wherein preliminary outflow openingsare provided in the lower side wall area of the diffuser.
 8. Airbagmodule according to claim 7 wherein the preliminary outflow openings arearranged so that there is no overlap with outflow openings of the gasgenerator.
 9. Airbag module according to claim 7 wherein the preliminaryoutflow openings are provided above the outflow openings of the gasgenerator.
 10. Airbag module according to claim 7 wherein the overallcross-sectional area of the preliminary outflow openings is smaller thanthe overall cross-sectional area of outflow openings of the gasgenerator.
 11. Airbag module according to claim 7 wherein fourpreliminary outflow openings are provided.
 12. The airbag module ofclaim 1, further comprising slits positioned in the central side wallarea to allow for deformation of the central side wall.
 13. The airbagmodule of claim 1, further comprising preliminary gas outflow openingslocated in the lower side wall area of the diffuser.
 14. The airbagmodule of claim 13, wherein the cross-sectional area of the preliminarygas outflow openings is less than the cross-sectional area of theoutflow openings.
 15. Airbag module according to claim 1 wherein thecentral wall area is formed with a plurality of portions which arereduced in structural rigidity and which render the central side wallarea deformable.
 16. Airbag module having a gas bag, gas generator and amodule cover having a tear-open area is arranged above the gas generatorwherein: the gas generator is mounted in a diffuser which encloses thegas generator and is provided with outflow openings, and the diffuserextends in a side wall area at a distance from the gas generator, theside wall area thereby extends beyond the gas generator upwards towardsthe tear-open area of the module cover and encloses at leastsubstantially the same cross-section along the side wall area adjacentthe gas generator, wherein the diffuser has a stepped construction witha lower side wall area, an upper side wall area and a central side wallarea which connects the upper wide wall area and the lower side wallarea, wherein the lower side wall area extends a distance from the gasgenerator and beyond the gas generator towards the tear-open area of themodule cover, the diffuser has in an upper side wall area a smallercross-sectional surface than the gas generator and in this area theoutflow openings are provided for the gases of the gas generator todischarge into the gas bag transversely to a longitudinal axis of thediffuser, wherein the central side wall area is deformable, wherein thecentral side wall area has material weaknesses, and wherein the centralside wall area has slits as the material weaknesses.
 17. Airbag moduleaccording to claim 16 wherein the slits have a width of approximatelyzero millimeters.
 18. Airbag module according to claim 16 wherein theslits run radially across a circular cross-section of the diffuser. 19.An airbag module comprising: an airbag; a gas generator mountedessentially coaxially in a diffuser having outflow openings to allow gasto flow into the airbag; a module cover having a tear-open area toaccommodate the airbag during inflation; wherein the diffuser has agenerally stepped construction extending toward the tear-open area ofthe module cover and includes a lower side wall, an upper side wallincluding the outflow openings positioned to discharge gas in adirection generally transverse to the upper and lower side walls, adeformable central side wall which is connected between the upper andlower side walls and which defines a stepped portion separating theupper side wall and the lower side wall, and wherein the upper side wallhas a smaller cross-sectional area than the gas generator.
 20. Theairbag module of claim 19, wherein the upper side wall includes an upperedge forming a top surface of the diffuser and the module beingconfigured so that prior to inflation the airbag is folded so that onlyone layer of the airbag overlies the upper edge.
 21. Airbag module asset forth in claim 18, wherein the upper side wall is essentiallycoaxial with the lower side wall.
 22. Airbag module as set forth inclaim 21, wherein the gas generator is arranged essentially coaxiallywith the upper side wall and the lower side wall.
 23. Airbag module asset forth in claim 19, wherein the cross section of the upper side wallis essentially circular and the cross section of the lower side wall isessentially circular.
 24. Airbag module as set forth in claim 19,wherein the upper side wall is essentially cylindrical, the lower sidewall is essentially cylindrical, and the lower side wall has a radiallyextending flange formed thereon.
 25. An airbag module comprising: adiffuser having a lower essentially cylindrical wall; a gas generatorpartly enclosed by the lower wall; an upper essentially cylindrical wallwhich is essentially coaxial with the lower wall and which has adiameter less than that of the portion of gas generator enclosed by thelower wall; and a deformable wall portion having a structure whichreduces its resistance to deformation with respect to the upper andlower walls and which allows the upper wall to be displaced toward thelower wall upon the application of a predetermined amount force.
 26. Anairbag module as set forth in claim 25, wherein the deformable wallportion includes a plurality of slits which have an essentially zerowidth.